1. Field of the Invention
The present invention relates to a ground connecting apparatus for a mobile terminal, and more particularly to a ground connecting apparatus for a mobile terminal in which grounds are directly or indirectly connected so as to reduce an Specific Absorption Rate (SAR) value, thereby adjusting a connection length of the grounds.
2. Description of the Related Art
Generally, in order to satisfy various requirements of consumers, mobile communication devices have been developed to provide multiple functions including voice communication, radio reception, and, MP3 music download via the Internet, and now provide access to various data including images through the use of cellular phones, PDAs, computers and notebook computers via data digitization. Such data are band-compressed using sound or picture technologies, and are then easily and efficiently transferred to various mobile communication devices via digital wireless communication or digital wireless broadcasting. These mobile communication devices include an HHP (Hand Held Phone), a CT-2 cellular phone, a smart phone, a digital phone, a PCS phone, a PDA (Personal Digital Assistant), and a notebook computer, etc.
Mobile communication devices are divided into several types according to their external shapes. An LCD is generally used as a data output unit. A keypad for inputting data includes a plurality of keys arranged in an array. Further, an antenna unit for receiving a signal transferred from a counterpart is installed at a suitable position on a main body of the mobile communication device. An essential object of the antenna unit is to increase efficiency thereof, and problem of the antenna unit to be solved is the decrease in SAR (Specific Absorption Rate).
The antenna units of conventional mobile terminals are divided into external antennas installed on the outside of the main body of the mobile terminal, such as a whip antenna, a helical antenna, a sleeve antenna, an N-type antenna, a chip antenna, a Frequency Shift-Planar Inverted-F Antenna (FS-PIFA), etc., and internal antennas installed on the inside of the main body of the mobile terminal, such as an inverted F-type antenna, a planar inverted F-type antenna, a diversity antenna, a microstrip antenna, a twisted loop antenna, etc. Further, the antenna units of the mobile terminals are divided into monopole antennas and planar antennas having a planar structure according to methods of exciting radiated electromagnetic waves. The monopole antennas include external antennas, such as whip antennas, helical antennas, sleeve antennas, chip antennas, and N-type antennas; and the planar antennas include inverted F-type antennas, planar inverted F-type antennas, diversity antennas, microstrip antennas, and FS-PIFAs. Here, the above-described monopole antennas are external antennas. On the other hand, a semi-exposed fixed-type monopole antenna which was recently developed, an internal monopole antenna employing a wave absorber, and a monopole antenna for a folder-type terminal for decreasing an SAR value are internal antennas, and have a broadband property and a low SAR value. The semi-exposed fixed-type monopole antenna has excellent efficiency, but has a reduced effect on the value of the SAR lower than that of the internal monopole antenna employing the wave absorber. The internal monopole antenna employing the wave absorber has an excellent reduction effect of the value of the SAR, but has efficiency lower than that of the semi-exposed fixed-type monopole antenna. Further, the semi-exposed fixed-type monopole antenna, the same as the conventional whip antenna, is disadvantageous in that it is difficult to perform impedance matching due to an enlarged coupling portion between the antenna unit and the folder of the mobile terminal. In addition, radiation efficiency is reduced by approximation between the antenna unit and a user's head, and a ground area having a designated size is required. Accordingly, it is difficult to reduce the thickness of the mobile terminal employing the semi-exposed fixed-type monopole antenna. The above monopole antenna for the folder-type terminal for decreasing SAR is proposed to solve these problems, thus having good properties both in the antenna efficiency and the reduction of the SAR value.
However, the above monopole antenna for the folder-type terminal for decreasing the SAR is designed such that the wave absorber is located at a position adjacent to a hinge connection unit installed at a folding portion between a main body and a folder of the terminal, thereby increasing the SAR due to the leakage of electromagnetic waves via the folding portion. As shown in FIGS. 1 and 2, a folder-type mobile terminal comprises a main body 10 including a plurality of keys 11 allowing a user to input desired data by pressing the keys, and a microphone 12. The folder-type mobile terminal further comprises a folder 20 including a main LCD 21 for displaying the input data, and a speaker 22. The main body 10 is connected to the folder 20 about a hinge axis (A1), and a hinge unit 30 is installed such that the folder 20 is rotated to be opened from and closed to the main body 10 centering on the hinge axis (A1). The main body 10 further includes a first PCB 13, and a main body-side ground 14 formed on the first PCB 13. The folder 20 further includes a second PCB 23, and a folder-side ground 24 formed on the second PCB 23. The hinge unit 30 includes side hinge arms 31 respectively installed at both sides of the main body 10, and a central hinge arm 32 installed on the folder 20 so that it is rotatably connected to the side hinge arms 31. A hinge module 50 is installed in the central hinge arms 32.
As shown in FIG. 1, an antenna unit 40 is installed at a designated position of the upper end of the main body 10, and the first PCB 13 is installed in the main body 10. The main body-side ground 14 is installed on the first PCB 13. A main LCD 21 is provided on the front surface of the folder 20, and a sub LCD (not shown) is provided on the rear surface of the folder 20. The second PCB 23 is installed in the folder 20. The folder-side ground 24 is installed on the second PCB 23.
In the conventional folder-type mobile terminal, in order to widen the folder 20 or contribute to the convenience in a process for manufacturing the terminal, the antenna unit 40 is installed on the upper surface of the main body 10 adjacent to hinge axis (A1).
Accordingly, electromagnetic waves from a feeder unit of the antenna unit 40 are leaked via a gap between the main body 10 and the folder 20, thereby raising the SAR value.
In accordance with conventional research results of the antenna employed by the folder-type mobile terminal products, the connection of the upper and lower portions of the folder converts the radiation properties of the antenna unit into directivity and disperses electric current density, which is concentrated at the gap between the main body and folder. Most of the folder-type mobile terminals are designed such that a data cable passes in the opposite direction of the antenna unit, and the main body-side ground 14 and the folder-side ground 24 are connected. In cases in which the main body-side ground 14 and the folder-side ground 24 are connected at a position adjacent to the antenna unit, a gain of the terminal is reduced and radiation toward a user's head in proportion to the reduction of the gain is decreased. The above results are obtained by directly connecting the main body-side ground 14 and the folder-side ground 24 at the position adjacent to the antenna unit or by connecting the main body-side ground 14 and the folder-side ground 24 in a call connection state.
However, since the conventional connection of the grounds employs a method of electrically and directly connecting the grounds only for reducing the SAR value, it is possible to directly connect the main body-side ground and the folder-side ground in the folder-type mobile terminal only at both ends of the hinge unit. In cases in which the direct connection of the grounds is performed at the above position adjacent to the antenna unit, the gain of the terminal is remarkably reduced, and thus field performance of the antenna unit deteriorates.
Further, the reduction of the gain and the radiation properties, such as the decrease of radiation toward the user's head, influence a position, a length and a thickness of a connection portion of the grounds, thus not being capable of allowing the antenna unit to obtain a desired result.